Expanded silicate particles



United States Patent 3,450,547 EXPANDED SILICATE PARTICLES Robert H. Sams, Aidan, and Newton W. McCready, Newtowu Square, P a., assigiiors to Philadelphia Quartz glrgigglalg'nlggwgglseyusggg uare, Philadelp ia, 5 of intumesced particles of the highest quality. When dried No Drawing. Filed Apr. 5 1966 Ser No. 540 211 to about to 15 water at these high ratios, the colloidal Int C1. 1 3 5 16 soluble silicates do not mturnesce to a large volume with U,s (3 ;...75 9 Claims high insulating value. However, we have found that if 10 we use a commercial soluble silicate with a ratio of about 2.0 to 3.2, excellent intumescence is obtained. The initial particles expand 30 to 100 times and may have a thermal ABSTRACT OF THE DISCLOSURE conductivity of about 0.029 B.t.u./in.- F., but the ex- Expanded particles of sodium silicate having a density Panded Particles are weak and friable l e y t between about 9 and 10 lbs./ t. an a compression reered' we have now Q P F h we add sistance 40 to 60 times greater than previous expanded amOFPhQUS form of 51116? 1S f h of largely particles f Sodium silicam are formed by heating a mi solving in the soluble Sill C816 leaving ittranslucent, we ture of sodium silicate, soluble silica and asbestos fibers can P only rcadlly mlx the alkah t a carefully below about 2500 C. formming particles and expanding restricted amount of asbestos fibers which will permit the said particles by intumcscence optimum expansion on intumescence, but can also retain said optimum expansion and the soluble silica will apparently become dissolved in the final stages forming what is effectively a high ratio alkali silicate in the range of 3.5 PRIOR ART to 5.0 and thereby will be much more resistant to solution The property of hydrated alkali silicate solids to exand Weathen'ngpand many times in volume and solidify in a forameniferour final P o 15 formed ot about 100 o 15 ous form is well known and has been employed in many R f of combined alkali metal o' h amorphous patents. The use of these expanded products for nonin u Proporuons as f required, In h ease of flammable fire-resistant insulation for heat and sound as Sodlum sllleates, for a fiftal ratio of -5 to sloalNaao well as translucent fire-resistant decoration is also widely (P y about a who of and to 3 Parts known but, because these products are attacked by mois- (P y about 2 P o asbestos h '8 ture, are exceedingly friable and exhibit low resistance to amount of 'flshestos fi rs l ret rd or Inhibit the excompression in their extended state, they have failed to Panelon mtumeseenee and a f r o nt 111 not attain the commercial acceptance generally expected of Strengthen the fibers 40 Or 50 es t Of t e unimth proved product.

It l h b ll k o t dd fill of ili The initial mixture is heated to dissolve at least part of silicates, and other non-reactive as well as reactive powthe Silica Without extensive pp b moisture o ders, and especially to add varying proportions of inat about for Several hours or y forced heating organic fibers to improve the physical properties of the t about for one ou of y othel' eomparahle expanded i t d product Th fill are d h 40 time and temperature conditions. This semi-translucent the final product and do not expand, resulting in a residue matetlal lshfokeh P and We Prefer to use the 8 to P of higher density and lower insulating value. Asbestos mesh fl'actloh for intumescence as the l P t 15 fibers have been used over a very wide range of concenh reuthly handled- However, y oonyement p 't tration to thicken the plastic alkali silicate and strengthen Slze y ho Such as 4 to 65 These Partleles h final product, whi h h d b we h f d h are heated individually to a rather high temperature of may also interfere with the expansion of the silicate. Furabout Q 9 hlghef- Thls may he done y allowing ther, it is well known to control the water content below them to falhlhdlyldually on a p e of y other means about 20% before the intumescence is brought about. Well-known f the our Product W111 have an PP In particular, sodium silicates containing a reactive Pe o y of about 9 o 10 lbs/cu. ft. and a comsilica such as diatomite form an expanded silicate having presslohfeslstanee of about 40-50 P' -y :That 18 Phollt 40 a somewhat higher silica to alkali ratio. In other cases t 50 tunes h strength o th oflgmal ummPl'oVed hollow glass spheres of soluble silicate containing an lntumeseed P t 0f elkah Slheateinsolubilizing agent, such as borate, have been formed by These mdludual Potholes ey be dll'ectly as adding a blowing agent. sulation,.for instance, by pouring them into a prepared In a number of cases silicon metal has been added P are Strong enough and tough enough to Steed to mixtures of sodium silicate and sand or other additives .Shoyelmg and p f Wlthouf f g, and o Wlll to form a bonded cement structure and sodium silicate hot Crush under h Welght m ordlnary Walls, has been used to cement hollow glass spheres into a solid as has ooourfed h e P u mass and expanded silicate particles have been embedded The hlghel' etteetlye 3150 a es he Water 1':- i abinder, sistance to such an extent that these stronger, tougher Thus the prior art is exceedingly complex, and exam- Particles h be used as hght'weight aggregate for ples of almost any conceivable additives can be found. ei e- It is therefore surprising that we have been able to make It IS Often d a l t prepare Such insulation in a an outstanding improvement over intumesced particles form Whieh y be ed and Still retain its exact form previously known by our discovery of a complex com- 5 and shape. We therefore include in our invention the position not previously disclosed. bonding of these particles with additional soluble silicate.

While most of these additives have also been used in We have found that the use of ordinary commercial silicontinuous layers of intumesced silicate, it is recognized cates is unsatisfactory as it is difiicult to form and dry the that the properties required in a composition for forming particles bound in this way without deterioration of the isolated particles are different primarily because of the particles and subsequent increase in density and loss of difference in the necessary heat treatment and the void characteristics.

3,450,547 Patented June 17, 1969 OUR INVENTION We have now found that the ordinary soluble silicates of commerce, even those with the highest available ratio, i.e. 3.3 to 3.8 SiO, to N330, do not permit development irsulation value.

We have found that a binder consisting, for example,

of a commercial sodium silicate having a ratio of about 3.2 to 4.0 when used with the addition of about 2% asbestos fibers will permit the intumesced particles to be wetted, formed, and dried even at temperatures of 110 C. without increasing the density unduly and the product may have a density of about 9 lbs/cu. ft. and an increased compression resistance of 60 p.s.i. or more.

We have further found that when we include in the binder additionally 0.1 to 0.3% of silicon metal or ferrosillicon alloy in finely divided condition, such as 100 to 400 M (preferably 325 mesh X down), the final product will still have a density of about 9 lbs/cu. ft. but the compression resistance will be further increased to about 100-110 p.s.i. or higher, even though there may be no evidence of :any voids by reaction between the silicon and the alkali silicate which is known to react with the formation of additional alkali silicate and hydrogen gas and tends to expand the film.

We are aware, further, that the properties of our product may be improved by the addition of borates and phosphates soluble in the alkali silicate. These are expected to toughen and strengthen dried films of such alkali silicates. .ludicious use of other reactive fillers, such as zinc oxide and dolomite, may be included to increase weather re-' sistance but any reaction which results in a silica gel will lower the strength of the final structure. Various silicone coatings are also applicable.

EXAMPLES The materials used in the following examples are described as follows.

The soluble silicates obtained from the Philadelphia Quartz Company had the following characteristics:

G-a spray dried product having approximately 19.5% Na,0, 63.0% SiO and 17.5% water, with an apparent density of 55 lbs/cu. ft. and a particle size approximately 100 mesh.

RU-a liquid sodium silicate having a ratio of 2.4 SiO to Na O by weight, about 13.85% of Na 0, and a viscosity of about 21 poises.

N-a sodium silicate having a ratio of 3.22 SiO /Na O by weight with about 8.9% of Na O and a viscosity of about 1.8 poises.

O-a sodium silicate having the same ratio as N but with about 9.2% Na o and a viscosity of about 4 poises.

S35a sodium silicate having a ratio of 3.75 SiO /Na O with about 6.75% N330 and a viscosity of about 2.2 poises.

Diatomaceous earth was Celite #503 obtained from Iohns-Manville. The asbestos fibers were acid-washed Powinco Asbestos Fiber obtained from Arthur H. Thomas Co. The silicon powder was a finely divided product obtained from Electrometallurgical Co.

EXAMPLE 1 (a) The fine, white powder, G sodium silicate, was sprinkled onto an inclined heated metal surface so that the individual particles expanded and were collected at the bottom of the inclined heated metal. This collected soft, white powder had a density of 5 lbs./cu. ft. and, when tested with a Thwing-Albert Tensile Tester using a plunger having a surface area of 2 sq. in., was found to have a resistance to compression of only 1 p.s.i. when the plunger was forced to a depth of 0.4 inch in an original depth of 1.5 inches. A typical polystyrene foam has a density of about 2 lbs/cu. ft. but it has a compression resistance of about 45 p.s.i. when tested the same way.

(b) Even when the G silicate was reduced in moisture content to and expanded by said heating in the same way to a product having a density of 7.4 lbs/cu. ft. the resistance to compression was not appreciably increased. Furthermore, the very finely divided spray-dried G sodium silicate results in particles which are too small to have the highest utility.

(c) Twenty-two parts by weight of Celite #503 diatomaceous earth were dispersed in 100 parts of RU sodium silicate. The overall ratio of the composition was 4 SiO, to 1 Na O. This was heated with minor loss of water at 95 C. in the oven overnight and cooled and crushed. A fraction of 8 to 10 mesh was separated and these particles were heated suddenly as before. The best product was produced by drying to 11.5% of H 0. However, on rapid heating in the usual way the particles were practically as light weight and fragile as the original expanded granules without the addition of the diatomaceous earth. Even granules of this type expanded to half the full diameter were almost as fragile as those completely expanded.

-"(d) When sutficient diatomaceous earth was added to raise the ratio to 6 SiO,:l Na O the product did not expand when heated suddenly. When 10% of the weight of the silicate was added as asbestos the expansion on heating was restrained to practically nothing.

EXAMPLE 2 However, using the mixture of 100 parts of RU sodium silicate, 10 parts of water, 22 parts of Celite #503 diatomaceous earth, and 2 parts of asbestos fiber; allowing the mass to react at 95 C. without evaporation for 10 or 12 hours, cooling, crumbling and screening; particle fractions of 4' to 8 mesh, 8 to 19 mesh, and 10 to 14 mesh, all expanded to porous spheres with densities ranging from -8.5 lbs./cu. ft. for the 12 and 14 in. mesh particles to 10 lbs/cu. ft. for the 4 to 8 mesh particles which had expanded to Mt inch diameter. The larger spheres were the stronger individually but when tested under compression as a mass of loose spheres the smaller spheres were more resistant. Therefore, the fraction from 8 to 10 mesh was preferred. It had a density of 9.6 lbs./cu. ft. and compression resistance of about 60 p.s.i. whereas the 10 to 14 mesh fraction produced only 40 p.s.i.

EXAMPLE 3 parts of RU sodium silicate was mixed with 22 parts of Celite #503 diatomaceous earth and 2 parts of acid washed asbestos fiber. This formed a paste which was heated for 2 hours at about 250 F. under pressure to avoid loss of water. After the reaction period the product was cooled and crushed and the 8 to 10 mesh and 4 to 35 mesh fractions were expanded by heating on a hot metal surface as before.

These puffed silicate beads were bonded together into a mold. It the beads were coated with straight sodium silicate, such as O 3.2 SiO,:Na,O rat-i0 sodium silicate at 42 Baum, the liquid bonding medium tended to expand on quick-drying forming a bond much weaker than the beads themselves. When the beads were wetted wit-h the same ratio silicate at 41 Baum and allowed to set overnight in a mold some bonding was accomplished by drying at C., but if oven drying was attempted the interior of the mold became too wet and the beads dissolved and flowed together. However, if the beads were coated with a bonding solution of 90% S-35 sodium silicate diluted with 10% of water and dried at 110 C., a block of the 8-10 M fraction having a density of 9 lbs/cu. ft. was obtained with a compression resistance of about 60 lbs./ sq. in. for an indentation of 0.4 inch.

This bond was improved by mixing 5 parts of silicon powder with the 90 parts of S-3S and 10 parts of water as the bonding solution, and drying as before. There was no apparent indication that the silicon particles reacted and no evidence of expansion of the bonding coating. However, the compression strength rose to 110 lbs./sq. in. for a compression of 0.4 inch. If the bonding solution had been used without heating at 110 or possibly with less water in the silicate, the bond would have expanded to fill the voids since a beaker of such composition did expand overnight.

The silicon may be added to the silicate itself or be first dispersed in water and then added to the silicate.

The presence of about 1.5 to asbestos fibers in the coating solution helped prevent the silicon particles from settling into a compact, unreactive layer. With 1.5 to 3% asbestos, the film will expand.

Of course, it is recognized that other bonding media, such as waterproof resorcinol formaldehyde resins, might be used to combine the porous spheres into a block with increased resistance to water.

More or less detailed claims will be presented hereinafter and even though such claims are rather specific in nature those skilled in the art to which this invention pertains will recognize that there are obvious equivalents for specific materials recited therein. Some of these obvious equivalents are disclosed herein, other obvious equivalents will immediately occur to one skilled in the art, and still other obvious equivalents could be readily ascertained upon rather simple, routine, non-inventive experimentation. Certainly no invention would be involved in substituting one or more of such obvious equivalents for the materials specifically recited in the claims. It is intended that all such obvious equivalents be encompassed within the scope of this invention and patent grant in accordance with the well known doctrine of equivalents as well as changed proportions of the ingredients which do not render the composition unsuitable for the disclosed purposes. Therefore, this application for Letters Patent is intended to cover all such modifications, changes and substitutions as would reasonably fall within the scope of the appended claims.

What is claimed is:

1. The process which comprises:

(a) mixing an alkali metal silica having an SiO, ratio between about 2.0 and 3.2 with a sufficient amount of an amorphous form of silica to give an overall SiO-,-:Na,0 ratio of about 3.5 to 5.0,

'(b) heating the admixture of (a) to a temperature between about 95 C. and 250 C. so as to dissolve at least part of the silica without extensive or appreciable moisture loss,

(c) admixing about 100-150 parts of the heated product of (b) with about 1.5 to 3 parts of asbestos fibers,

(d) cooling and breaking up the product of (c) into particles within the range of about 4 to 65 mesh,

(e) heating individual particles resulting from (d) at a temperature of at least 400 C. so as to cause intumescence of the particles, and

'(f) recovering high-strength intumesced particles having (1) an overall ratio of about 3.5 to 5.0 SiO, to

N320 (2) a density of about 9 to 10 lbs/cu. ft., and (3) a compression resistance of about 40 to 2. The process of claim 1 wherein said amorphous silica is diatomaceous earth.

3. The process of claim 1 wherein the Si0,:Na,O ratio of the final product is about 4.

4. The process of claim 1 wherein two parts of asbestos fiber are mixed with about 122 parts of the heated productof'(b). I

5. The process of claim 1 wherein the size of the particles heated to in-tumesoence in step (e) is between 8 and 10 mesh.

6. High-strength intumesced articles useful as insulation material and as a lightweight aggregate composed of:

(a) about to parts of sodium silicate and an amorphous silica,

(b) about 1.5 to 3 parts of asbestos particles; and

having:

(1) an overall ratio of about 3.5 to 5.0 SiO, to N330, (2) a density of about 9 to 10 lbs./cu. ft., and (3) a compression resistance of about 40 to 60 7. An insulating block comprising the intumesced par- I ticles of claim 6 bound together with an adhesive comprising an alkali silicate having an SiO:Na O ratio of about 3.5 to 4.0, said block having a density of about 9 lbs./cu. ft. and a compression resistance of about 60 p.s.i.

8. The product of claim 7 in which the binder includes about 1.5 to 10% asbestos fibers.

9. An insulating block according to claim 7 having included in the binder 0.1 to .3% of a material selected from the group consisting of silicon and a silicon alloy, the final product having a specific gravity of about 9 lbs./ cu. ft. and a compression resistance of about 100-110 p.s.1.

References Cited UNITED STATES PATENTS 3,150,988 9/1964 Dess et al. 106-75 3,184,371 5/1965 Seidl 106-75 JAMES E. POER, Primary Examiner.

- US. Cl .X.R. 

